Process for producing web sections from a flexible web material as well as for producing packing containers

ABSTRACT

A process produces web sections from a flexible web material. The flexible web material is provided with tear-off lines at the distance of the length (L) of the web sections to be formed, which tear-off lines weaken the web material but do not bring about a complete separation of the web sections from the web material. The web sections are separated from the web material along the tear-off lines by tearing. The web material comprises a fabric made of small stretched plastic bands, and the tear-off lines are produced by laser beam processing.

The invention relates to a process for producing web sections from aflexible web material, wherein the web material is provided withtear-off lines at the distance of the length of the web sections to beformed, which tear-off lines weaken the web material but do not bringabout a complete separation of the web sections from the web material,and the web sections are separated from the web material along thetear-off lines by tearing.

Furthermore, the invention relates to a process for producing packingcontainers using web sections produced according to the invention, withan important aspect of the invention pertaining to the production ofside-gussetted containers, in particular side-gussetted bags.

The manufacture of side-gussetted packings from paper has been known formany decades. In practice, such packings are produced according to thefollowing method:

-   -   A flat paper web is provided with straight or stepped        perforation lines at the distance of the later section length.    -   The flat web is formed into a tube and stuck together        longitudinally.    -   Subsequently, the tube sections are separated by tearing them        off along the perforation lines.    -   An end region of the tube section that has been torn off is        formed into a bottom and stuck together.

The construction of a “pinch bottom packing” is known, for example, fromU.S. Pat. No. 4,008,850, wherein, in said document, it is also suggestedthat a plastic-coated paper be used for the web material and thatplastic-coating surfaces be stuck together.

A device for producing multi-ply paper bags comprising tube sectionswith a staggered arrangement of the individual paper layers is knownfrom the document EP 664208. In order to be able to produce differentformats of paper bags, the “tubing machines” used therefor exhibitvariability of the distances between the transverse perforations in theindividual paper layers, which distances determine the lengths of thetube sections. The distances between the transverse adhesive tapesextending in a transverse direction are also adaptable accordingly. Theknown device for producing a multi-ply tube from paper webs providedwith transverse perforations at equal distances, from which tubesections are torn off for bag production, comprises perforating knivessupported in a machine frame and fixed to a rotating shaft, whichprovide the paper webs with transverse perforations, wherein the radialdistance of the perforating knives to the shaft is variable for formatadjustment. Furthermore, transverse adhesive cylinders provided withtransverse adhesive strips and cooperating with adhesive applicationdevices are supported in the machine frame. Using a longitudinaladhesive roll, the overlapping edges of the paper webs are provided withan adhesive coating before they are turned over by guide rolls to formtubes. Four supports for perforating knives, which are optionallyattachable thereto, are arranged on the rotating shaft at equal angulardistances, the perforating knives having means for adjusting theirradial distance to the shaft.

Placing perforation lines on paper bags is not very problematic sincepaper can be cut easily. In contrast, however, placing the perforationis a great challenge when side-gussetted packings are produced fromsynthetic fabrics or composites thereof, since cutting is problematic incase of synthetic fabrics with small bands lying on top of each other.For example, expensive punching tools, which are not very flexible andare susceptible to wear, have so far been required. Fabrics made ofsmall stretched plastic bands are affected by those problems even ifthey are linked to at least one additional material layer which involvesa coating of the small plastic bands or of the fabric or compounds ofthe fabric with other materials. Fabrics and their composites are oftenproduced as tubular webs. It would also be desirable to find a processby means of which an offset perforation can be placed directly on saidtubular webs.

The present invention solves the above-mentioned problems of the priorart by developing further the initially mentioned process for producingweb sections from a flexible web material, which is a fabric made ofsmall stretched plastic bands, by producing the tear-off lines by laserbeam processing. Using a laser beam, it becomes possible to cut a fabricof small plastic bands, to perforate it or to scratch it with a definedpenetration depth, although the thickness of the web material varies dueto the arrangement of the small bands in the fabric at least partiallyon top of each other. A further advantage is that lasers are verylow-maintenance and almost wear-free. Preferably, the fabric is producedfrom single- or multi-layered small plastic bands made of PP, PE or PET,wherein, in most cases, the small plastic bands are stretched prior toweaving in order to multiply their strength.

Due to the process according to the invention it is possible—in contrastto the prior art—to design the tear-off lines as perforation lines orweakening lines or as a combination of perforation and weakening lines,thereby creating an excellent adjustment of the detachability to the webmaterials to be processed.

The document DE 4122273 A1 discloses a process for laser cutting ofcontinuously moved strips of a web or flat material. Continuous orperforated transversal (partial) cuts are thereby produced by laser inthe web or flat material. The placing of weakening lines is notdisclosed. Nor is it disclosed that the web sections are separated fromthe web material by tearing. Furthermore, the document contains nomaterial data with regard to the web or flat material. From the drawing,it is only apparent that the web material is single-layered.

The invention is excellently applicable for web materials comprising afabric of small plastic bands which is linked to at least one additionalmaterial layer, since the cutting capacity of the laser can be adjustedvery well to various material combinations.

In one embodiment of a fabric of small plastic bands which is providedwith at least one additional material layer, the additional materiallayer is a plastic layer such as, e.g., an OPP film, which is connectedto the fabric. In a further embodiment, the additional material layer isa coating of plastic material which is applied to the small plasticbands of the fabric. In yet another embodiment, the web material is acomposite material made of a fabric of small plastic bands, whichoptionally is coated, and at least one further composite componentselected from a plastic film, metal film, metallized plastic film,nonwoven fabric (nonwoven), specific adhesive layers and/or paper.Preferred materials comprise single- or multi-layered small plasticbands made of PP, PE or PET, wherein the fabrics produced from thesesmall plastic bands may be provided with a single- or multi-layeredcoating of PP, PE or specific adhesive layers. The external individuallayers of such a composite may also be provided with external printingor reverse printing.

A particular advantage of the invention is that it is also applicablefor a tubular web material. In order to have the possibility toperforate the tube's two layers lying on top of each other in differentlocations, thus placing a staggered perforation directly on a tube, itis provided that the web material of the two opposing outer surfaces issubjected to laser beam processing.

Of course, the invention is also applicable for a flat web material.

In a preferred embodiment of the invention, the laser beam is guidedthrough a scanner unit along the predefined tear-off line, wherein, incase of a tubular web material, laser sources and scanner units may bearranged on the top side and on the bottom side of the tubular web. Bydeflecting the laser beam with a scanner it becomes possible to movealong almost any desired outline of the tear-off line while the webmaterial is being moved under the laser, whereby the outline can veryeasily be adjusted to the dimensions of the packing in asoftware-controlled manner.

In order to realize different penetration depths or permeation depths ofthe laser beam into the web material, it is provided in one embodimentof the invention that, when the laser beam is being guided along thepredefined tear-off line, the laser energy (more precisely: the energydensity at the point of impact on the web material) is altered accordingto the intended penetration depths into the web material.

The invention enables the tear-off line to be produced while the webmaterial is being moved continuously by guiding the laser beam along insuch a way that the longitudinal motion of the web material iscounterbalanced, whereby the laser energy is optionally adjusted to therespective distance between the laser source and the point of impact onthe web material in order to always provide the desired laser energy atthe point of impact. It is possible to keep constant the energy densityat the point of impact with an expanding beam by adjusting the laserpower to the distance between the laser source and the web material.

For controlling the penetration depth of the laser beam into the webmaterial, it may furthermore be provided that the power of the lasersource is adjusted depending on the relative speed of the laser beamwith respect to the web material or that the relative speed of the laserbeam is adjusted with respect to the web material. The energy introducedinto the web material by the laser beam is thus determined per unit oflength of the tear-off line.

Furthermore, using the invention, any desired web section requiring astepped web end section can be produced, since stepped tear-off linescan be generated by the laser beam without any problems.

The process according to the invention for producing web sections from aflexible web material is excellently suitable for use in a process forthe production of packing containers, in particular side-gussettedpackings, wherein the web sections are torn off from the web materialafter the tear-off line has been produced in the web material by laser.For the manufacture of a bottom and a top surface, respectively, atleast one end region of the web section is folded over the web sectionbody and the end region that has been folded over is fastened to the websection body by gluing or welding. Folding-over can be done once orrepeatedly.

If a flat web material is used, the web sections are longitudinallyformed into a tube before they are torn off so that the longitudinaledges will overlap, which edges will subsequently be connected, inparticular glued or welded, to each other in order to produce alongitudinal seam.

For the production of side-gussetted packings, in particularside-gussetted bags, at least one longitudinal fold is formed in the websections, preferably before the web sections are torn off from the webmaterial.

The invention is now illustrated in further detail in a non-limiting waybased on exemplary embodiments with reference to the drawings. In thedrawings

FIG. 1 shows a perspective view of a tubular web material in whichtear-off lines are placed according to the invention;

FIG. 2 shows a top view of the tubular web material treated according tothe invention;

FIG. 3 shows a top view of a flat web material in which tear-off linesare placed according to the invention;

FIGS. 4 to 6 show perspective views of tear-off lines produced in a webmaterial according to the invention;

FIG. 7 shows the application of scratching as illustrated in FIG. 6 plusperforating for a flat web made of a compound consisting of a fabric ofsmall plastic bands and a film;

FIG. 8 shows the application of perforating as illustrated in FIG. 4 fora tubular web made of a compound consisting of a fabric of small plasticbands and a film.

At first, the process according to the invention for producing websections 2 from a flexible web material 1 is now illustrated withreference to FIG. 1. The flexible web material is conveyed to aperforating station in the longitudinal direction (arrow A) byconventional means of conveyance, for example, roll pairs (notillustrated). In said exemplary embodiment, the web material 1 istubular, being flatly folded so that an upper (1 a) and a lower (1 b)material web lie on top of each other. The web material 1 comprises afabric of small plastic bands which preferably consist of PP, PE or PETand suitably were stretched prior to weaving. The small plastic bandscan have a single- or multi-layered design. The fabric can be linked toat least one additional material layer. In one variant, the additionalmaterial layer is a single- or multi-layered plastic layer, inparticular made of PP, PE, or an OPP film, or comprises specificadhesive layers. In a further variant, the additional material layer isa single- or multi-layered coating of plastic material which is appliedto the small plastic bands of the fabric. In yet another variant, theweb material is a composite material made of a fabric of small plasticbands, which optionally is coated, and at least one further compositecomponent selected from a plastic film, metal film, metallized plasticfilm, nonwoven fabric (nonwoven), specific adhesive layers and/or paper.The external individual layers may also be provided with externalprinting or reverse printing.

The perforating station to which the web material 1 is conveyedcomprises two laser cutting units 7, each comprising a laser source 4for generating a laser beam 6 and a scanner 5 for deflecting the laserbeam 6. A first laser cutting unit 7 is arranged above the tubular webmaterial 1, with its laser beam directed at the outer surface of theupper material web 1 a. The second laser cutting unit 7 is arrangedunderneath the tubular web material 1, with its laser beam directed atthe outer surface of the lower material web 1 b. The two laser cuttingunits 7 have the function of providing the web material 1 with tear-offlines 3 a, 3 b at the distance of the length L (see FIG. 2) of websections 2 to be formed, which tear-off lines will indeed weaken the webmaterial 1 but will not bring about a complete separation of the websections 2 from the web material 1. The tear-off lines 3 a, 3 b producedin the web material 1 and the web sections 2 are illustrated in top viewin FIG. 2.

The two laser cutting units 7 operate independently of each other, withthe energy of the respective laser beam 6 being adjusted such that itcuts a tear-off line 3 a, 3 b only into the material web 1 a or 1 bassociated to it without, however, damaging the other material web 1 bor 1 a. The tear-off lines are shaped by the laser beam 6 as perforationlines 3 a-1 (see FIG. 4) or weakening lines 3 a-2 (see FIG. 5) or as acombination of perforation and weakening lines 3 a-3 (see FIG. 6).

After the formation of the tear-off lines 3 a, 3 b, the web sections 2can be torn off from the web material 1 and processed further in a knownmanner.

The tear-off lines 3 a, 3 b may have most diverse outlines, inparticular, they may be stepped multiple times. The laser beam 6 isguided by the scanner 5 along the outline of the tear-off line, whichoutline has been predefined by software, whereby said outline is easilychangeable and thus the process according to the invention displaysgreat variability. Using the invention, it is in particular alsopossible to control and alter the energy of the laser beam while saidbeam is being guided along the predefined tear-off line in order togenerate, for example, a combination of perforation and weakening linesor in order to keep constant the energy of the laser beam despite avariable distance between the laser source 4 and the point of impact ofthe laser beam 6 on the material web 1 a, 1 b. By controlling the laserenergy it is also possible to perforate material webs with changingmaterial properties (thickness, composition of the composite, etc.).

An additional advantage of the invention is that the web material 1 cancontinuously be moved further along direction A while the tear-off lines3 a, 3 b are being cut by the laser beam 6. In doing so, the laser beam6 is guided along the movement of the web material in such a way thatthe longitudinal motion (A) of the web material 1 is counterbalanced.Optionally, the laser energy can be adjusted to the respective distancebetween the laser source 6 and the point of impact of the laser beam 6on the web material 1.

The energy introduced per unit of length and hence the penetration depthare determined by the power of the laser source 4 and the relative speedof the laser beam 6 with respect to the web material 1.

Apart from in the tubular web material 1, tear-off lines 13 can also beformed in a flat web material 11 using the laser cutting according tothe invention so as to produce web sections 12 as illustrated in topview in FIG. 3. Only one laser cutting unit 7 is required for a flat webmaterial 11. It should be pointed out that, depending on the outline ofthe tear-off lines 3 a, 3 b, it might perhaps be possible to get by withone laser cutting unit 7 also in case of a tubular web material 1.

With the aid of the process according to the invention for producing websections 2, 12 from a flexible web material 1, 11 by laser cutting, itis possible to manufacture packing containers by first producing the websections 2, 12 by generating the tear-off lines 3 a, 3 b, 13 andsubsequently tearing off the web sections 2, 12 from the web material 1,11, thereafter folding at least one end region of the web section 2, 12over itself and over the web section body, respectively, once orrepeatedly and fastening the end region that has been folded over to theweb section body by gluing or welding. If a flat web material 11 isused, the web sections 12 are longitudinally formed into a tube withoverlapping longitudinal edges before they are torn off, which edgeswill be connected, in particular glued or welded, to each other.

Furthermore, in the material tube that has been produced, at least onelongitudinal fold 8 can be formed in the web sections 2, 12, preferablybefore the web sections 2, 12 are torn off from the web material 1, 11.Side-gussetted packings, in particular side-gussetted bags, can thus beproduced.

FIG. 7 shows the application of the method described in FIG. 6(weakening plus perforated sections) for a flat web consisting of acompound made of a fabric of small plastic bands 9 and a film 10, e.g.,a plastic film, in particular an OPP film, or a metal film or metallizedplastic film. Thereby, the laser beam hits the fabric side (which willlater form the inside of the packing), cuts through most of the fabric 9but perforates the remaining film 10 only in a small number of locations(preferably in locations extending along the direction of the web). Itcan thereby be achieved that the web can later be torn off neatly at theperforation lines.

FIG. 8 shows the application of perforating as illustrated in FIG. 4 fora tubular web made of a compound consisting of a fabric of small plasticbands 9 and a film 10. Thereby, the laser beam hits the film side (whichwill later be the outside of a packing produced therefrom) and, insections, cuts through the web completely. The remaining ribs must benarrow, and possibly they are also weakened (scratched) as shown in FIG.6 so that, later, the tube sections can be separated neatly. Locationsextending along the direction of the web must in any case be cut throughcompletely and must not exhibit any ribs.

1. A process for producing packing containers, comprising: producing websections from a flexible web material, wherein the web material isprovided with tear-off lines at a distance of a length (L) of the websections to be formed, which tear-off lines weaken the web material butdo not bring about a complete separation of the web sections from theweb material, wherein the web sections are separated from the webmaterial along the tear-off lines by tearing, wherein the web materialis a fabric made of small stretched plastic bands and that the tear-offlines are produced by laser beam processing, wherein producing websections further comprises: guiding a laser beam through a scanner unitalong the predefined outline of the tear-off line, and when the laserbeam is being guided along the predefined outline of the tear-off line,altering the laser energy of the laser beam according to the intendedpenetration depths into the web material, tearing off the web sectionsfrom the web material, folding at least one end region of the websection over the web section body at least once, and fastening the endregion that has been folded over to the web section body by gluing orwelding.
 2. A process for producing packing containers according toclaim 1, wherein, if a flat web material is used, the web section arelongitudinally formed into a tube before they are torn off so that thelongitudinal edges will overlap and will subsequently be connected, inparticular glued or welded, to each other.
 3. A process for producingpacking containers according to claim 1, wherein at least onelongitudinal fold is formed in the web sections, preferably before theweb sections are torn off from the web material.